1. Crayon Rock Cycle - Background

Teacher Background
The rock cycle is perhaps the most basic, fundamental principle of geology. All rocks are related to each other and may be transformed from one kind to another. In its simplest form, the rock cycle describes the relationships between the 3 major types of rock:

  • Igneous Rocks - Formed from the cooling of molten rock (magma).
  • Sedimentary Rocks - Formed from layers of sediment as the pressure of overlying layers compacts the sediment into rock. Sometimes, a cementing agent, dissolved minerals such as silica or carbonates, helps bind the sediment particles together.
  • Metamorphic Rocks - Formed from other rocks that are exposed to intense heat and pressure and thus change their physical and/or chemical form.

Molten rock or magma solidifies either rapidly at the Earth’s surface or slowly under the Earth’s surface into igneous rock (this is the whole crayon we start with). As these rocks are exposed to erosion and weathering, they are broken down into sediment (a pile of crayon shavings). The grains of sediment may be transported long distances by water, wind or gravity, and eventually deposited in layers. As more and more sediment layers build up on top of each other, the sediments are compacted and sometimes cemented together into sedimentary rock (squishing the crayon shavings together) in a process called lithifaction. With heat and pressure (partial melting in hot water), the rock will undergo a physical and/or chemical change into metamorphic rock. If the rock is melted completely and cooled, you once again have igneous rock.

The rock cycle is attributed to James Hutton (1726-1797), the “father of geology” who meticulously explored and documented the landscape of the British Isles. Hutton proposed the principle of uniformitarianism, the idea that the processes that shape the world today also operated in the past. His idea brought abo